1. Field of the Invention
The present invention relates to transceivers and more particularly to a diplexer for a Ku-band satellite transceiver.
2. Background of the Invention
In transceiver design, there is a necessity to keep transmit and receive channels isolated. This is done using a diplexer at the front end or antenna port. This apparatus needs to provide isolation between transmit and receive ports, as well as filtering of unwanted local oscillator emissions and second harmonic products from the transmitter. This all needs to be accomplished while still maintaining a minimal loss and optimal impedance match.
There are other diplexer designs on a variety of materials and frequency bands. Typically, these prior art diplexers are configured on a two-layer material; however these devices do not have second harmonic suppression, nor are they small enough to be placed using automated manufacturing techniques as provided for in the present invention. These prior art devices use various architecture designs and materials. Examples of these diplexers are covered under the following U.S. Pat. Nos. 4,168,479 and 6,982,612.
FIG. 1 shows a diplexer design as disclosed in the prior art. Coupled line microstrip filters 10 and 12 are combined using microstrip transmission lines 14 and 16. A third microstrip transmission 18 is brought out to common antenna port 20. These items are typically etched using standard photolithographic processes on the microwave dielectric material. These prior art diplexer devices have several shortcomings such as large size and the failure to address the electromagnetic compatibility (EMC) issues of second harmonic and local oscillator radiation. In modern communication systems there is a requirement to meet EMC requirements for the European Telecommunications Standardization Institute (ETSI) and the Federal Communications Commission (FCC) in the United States. The conventional diplexer topology does not provide the additional out of band rejection necessary to meet these requirements.
Therefore, there is a need in the art for a diplexer that has an insertion loss in the receive band of less than one (<1) dB, an insertion loss in the transmit band of less than one (<1) dB, local oscillator rejection of twenty (20) dB or greater, and transmitter second harmonic suppression of greater than thirty (>30) dB. In addition, the diplexer needs to be compact to allow for easy integration into a transceiver. When used in a half duplex system, the diplexer should not be sensitive to the off state impedance of the power amplifier. This is accomplished by having as much isolation as possible between transmit and receive ports. The diplexer should be producible using standard lithographic processes and have metallization that can be reproduced in a repeatable fashion by a qualified supplier.